Bone Abstracts

Objectives: While studies in adults with cystic fibrosis (CF) showed increased fracture risk and decreased bone mineral density (BMD), the results of the pediatric studies have been contradictory. Our aims were to assess volumetric BMD, bone geometry and the muscle–bone relation at the forearm in children with CF using peripheral quantitative CT (pQCT), and to correlate these bone parameters to pulmonary function.

Methods: Fifty-three patients with CF (median age 12.9 years, range 6.7–18.8, 29 girls) were examined by pQCT at the non-dominant forearm. Results were expressed as Z-scores using published reference data. Median forced expiratory volume in one second (FEV1, % predicted) of the spirometry examinations performed during the last year before densitometry was selected as a surrogate of pulmonary function. The differences from reference data were tested by one-sample T-test, Pearson correlation coefficient was used to correlate pQCT-derived bone parameters with FEV1.

Results: Trabecular BMD was normal (mean Z-score −0.2±1.3, NS) in children with CF. Total bone cross-sectional area, cortical bone area and cortical thickness were all normal when adjusted for height (mean Z-scores 0.0±1.1, 0.0±1.0 and 0.0±0.8, respectively). Cortical BMD was increased (mean Z-score 1.0±0.9, P<0.001). As a consequence of decreased muscle area (MA, mean Z-score −1.5±1.5, P<0.001) the bone mineral content to MA ratio was increased (mean Z-score 1.3±1.0, P<0.001). Whereas FEV1 was positively correlated to muscle area (R²=0.20, P<0.002) and bone geometry (i.e. cortical thickness (R²=0.24, P<0.001) and cortical bone area (R²=0.20, P<0.002)), the correlation with BMD was weak (R²=0.08, P=0.035 and R²=0.007, NS for trabecular and cortical BMD, respectively).

Conclusions: Children and adolescents with CF have normal volumetric bone density and geometry at the radius but decreased muscle mass at the forearm. FEV1 seems to be a good predictor of changes in muscle area and bone geometry in children with CF.

Grant support: Supported by the project (Ministry of Health, Czech Republic) for conceptual development of research organization 00064203 (University Hospital Motol, Prague, Czech Republic).